isotopic mass

For Cl the isotopic mass is less than 35 so this must be the dominant factor.

This weighted average can be quite different from the near-integer values for individual isotopic masses.

The only difference is that relative isotopic mass differs is a pure number with no units.

Isotopic masses can play an important role in physics but physics less often deals with molecules.

Sometimes called a "Bainbridge mass spectrometer," this configuration is often used to determine isotopic masses.

Isotopes are specified with a number equal to the integer isotopic mass preceding the atomic symbol.

There are two reasons for the difference between mass number and isotopic mass, known as the mass defect:

Previously it was based on the mass of the mixture of naturally isotopic masses of carbon, oxygen, or hydrogen.

The mass number gives an estimate of the isotopic mass measured in atomic mass units (u).

Also in 1950, Maxwell and Reynolds et al. found that the critical temperature of a superconductor depends on the isotopic mass of the constituent element.

The masses used to compute the monoisotopic molecular mass are found on a table of isotopic masses and are not found on a typical periodic table.

The molecular mass can be calculated as the sum of the individual isotopic masses (as found in a table of isotopes) of all the atoms in any molecule.

Isotopic shifts are best known and most widely used in vibration spectroscopy where the shifts are large, being proportional to the ratio of the square root of the isotopic masses.

For example, the relative isotopic mass of carbon-12 is exactly 12, but (as in the case of atomic mass) no nuclides other than carbon-12 have exactly whole-number values in this scale.

Because these standard atomic weights are an average (mean) of relative isotopic masses for a given element from different sources (places on Earth), standard atomic weights are subject to natural variation.

In such cases, again, the isotopic mass can be important since the change in mass changes the vibrational frequencies for example but the monoisotopic mass is generally not relevant or at least uninteresting.

Thus, the relative isotopic mass is the relative mass of a given isotope (specifically, any single nuclide), scaled by the mass of carbon-12, which on this scale is set equal to 12.

Relative isotopic mass (not to be confused with relative atomic mass) has exactly the same numerical value as atomic mass when atomic mass is expressed in unified atomic mass units.

Relative atomic mass (not to be confused with relative isotopic mass) is a synonym for atomic weight, and in some circumstances may even be synonymous with standard atomic weight (depending on the sample, see below).

For this reason, the relative atomic masses of the 22 mononuclidic elements (which are the same as the isotopic masses for each of the single naturally occurring nuclides of these elements) are known to especially high accuracy.

This is an example of Aston's whole number rule for isotopic masses, which states that large deviations of elemental molar masses from integers are primarily due to the fact that the element is a mixture of isotopes.

A little more than three-quarters of naturally occurring elements exist as a mixture of isotopes (see monoisotopic elements), and the average isotopic mass of an isotopic mixture for an element (called the relative atomic mass) in a defined environment on Earth, determines the element's standard atomic weight.

The use of average atomic masses derived from the standard atomic masses found on a standard periodic table will result in an average molecular mass, whereas the use of isotopic masses will result in a molecular mass consistent with the strict interpretation of the definition, i.e. that of a single molecule.